In recent years, considerable effort has been directed toward the protection of workers from the high noise levels generated by industrial machines. When high speed machinery such as sewing machines are involved, noise reduction activities have been focused in two major areas. The first area of activity is in the redesign and engineering of the machines themselves to eliminate the noise at its source. However, the inherent nature of high speed sewing machines and economics of redesign place limitations on the practical potential of sufficiently reducing sewing machine noise. Furthermore, many existing machines have undesirably high operating noise levels. Hence, considerable activity has also been focused upon the development of noise attenuation structures for insulating the noise from a worker.
Attenuation of machine generated noise is complicated by the cooling requirements of high speed sewing machines. In most present day industrial sewing machines, the machine generated heat is at least partially dissipated by natural convection. Noise attenuation structures for protecting workers against high noise levels could interfere with the natural convection heat transfer mechanism and result in machine overheating.
Furthermore, it is necessary for the operator of a sewing machine to have access to the working machine components on occasions. Access to the thread tract of the machine is particularly important. Noise attenuating structures also tend to interfere with such access and/or require cumbersome disassembly and reassembly.
In U.S. Pat. No. 3,638,594 to Armstead, Jr. et al, a shroud is mounted to a frame and held in fixed relationship to a sewing machine. A fan is used to rapidly pass air through a relatively thin channel between the shroud and the machine at a high velocity to achieve efficient cooling. However, the shroud of Armstead, Jr. et al does not surround a sewing head and does not significantly attenuate noise generated thereby. Further, this prior art shroud is not readily removable by the operator to provide quick and easy access to the covered machine components.
A noise attenuating kit for enclosing an industrial machine is disclosed in U.S. Pat. No. 3,773,140 to Mahajan et al. This attenuating structure includes a number of panels rigidly fastened to major frame members of the enclosed machine. Slidable panels provide access to selected areas of the machine and are sealed to adjacent panels to prevent the escape of noise when closed.
U.S. Pat. No. 4,074,725 to Bader et al discloses a multicomponent hinged cover for attenuating noise generated by selected components of a weaving machine. The cover is folded about its hinges to provide access to covered machine components when required.